Conventional electromagnetic generators employ a moving coil of electrically conducting material, such as a wire immersed in a magnetic field. The movement of the coil in the magnetic field produces an electric current, as is well known. Energy losses are encountered by the passage of the generated electrical current through the wire conductors of the coil. These energy losses produce heat, which is basically generated at a rate equal to the current squared times its electrical resistance. The heat loss in such generators can be substantial. These losses can be significantly reduced in typical applications by using a generator which utilizes very low loss piezoelectric material which produces an electrical charge when mechanically stressed in a periodic fashion in place of the electromagnetic generator.
The piezoelectric effect is well known. This phenomenon produces an electric field within a suitable material when a mechanical force is applied. Conversely, if an electrical drive signal is applied to a piezoelectric material, a mechanical vibration results. As one can ascertain, such devices have been employed in resonators and other electronic or electromechanical devices. The piezoelectric effect has been widely investigated in the prior art and new materials are continuously being found.
As indicated above, high power generators, which can range from the 10 watt to multi-kilowatt range and utilize electrical wire, are extremely large and carry substantial weight. The use of piezoelectric materials and associated structures will result in a much lighter weight device, since the need for iron-based metallic structure is eliminated. Synthetic piezoelectric ceramics have been employed as transducing materials and have achieved reproducibility for many given compositions. These devices can be operated in various modes and basically can operate to convert stress or strain into an electrical field. Certain important piezoelectric ceramic materials include modified lead zirconate titanate (PZT) compositions and, to a lesser extent, modified barium titanate and lead titanate compositions. The use of, and properties of, piezoelectric ceramics are also well known.
It is, therefore, desirable to produce a high power generator employing low loss piezoelectric material which produces an electrical charge when mechanically stressed. In accordance with an aspect of the present invention, it is further desirable to implement a low/lowest possible output impedance to maximize power transfer to typical high power loads, which may be achieved by maximizing both the effective capacitance of the generating structure as well as the frequency of the prime mover acting on the generating structure.